1. Field of the Invention
This invention relates to apparatus for use in supplying a particulate material comprising a powdered thermoplastic resin to a flame spray gun.
2. Description of Related Art
Methods and apparatus for flame spraying thermoplastic resins onto substrates are previously known, having been disclosed for example in U.S. Pat. Nos. 4,632,309 and 4,934,595.
Application Ser. No. 07/760,866, filed Sep. 16, 1991 and assigned to the assignee of this application, discloses a feed assembly for use in a flame spray coating system comprising a powder source, a pressurized gas source, a pressure regulator for regulating a stream of gas from the pressurized gas source, an eductor for introducing powder into the stream of gas from the pressurized gas source, and means for selectively controlling the introduction of powder into the stream of gas from the pressurized gas source. In one preferred embodiment disclosed in application Ser. No. 07/760,866, the powder source comprises a gravity fed powder hopper communicating with the eductor assembly. The powder source and feed assembly disclosed therein is adapted to be attached to a backpack worn by the operator, or else mounted on a portable stand.
Powder hoppers for use with flame spray coating systems have also been disclosed that are adapted for use with multiple hoses and flame spray guns. Such systems are advantageous for some applications because several operators can work simultaneously using a single, larger volume powder source that can be situated away from the operators. One such application is in flame spraying a thermoplastic coating on the inside of large storage tanks. A stationary hopper containing a relatively large volume of powder can be situated outside the tank, and a plurality of hoses connected to the hopper can supply powder to flame spray guns used by different operators.
Notwithstanding the advantages of the flame spray coating systems previously known, difficulties have been encountered with powder feed systems that utilize a hopper in which a bulk quantity of powder comprising a thermoplastic resin is gravity fed to an eductor assembly that entrains the powder in a gas stream for delivery through a flow line to a flame spray gun. Bridging or clumping of the powder within the hopper can disrupt flow to the flame spray gun even when an adequate supply of powder remains in the hopper, causing inefficiency and unnecessary downtime.